Processing materials are used in a variety of industries to perform chemical reactions over a period of time. These processing materials have an inherent limit to their reactivity before the materials become depleted. Accurately monitoring the processing capacity of a processing material has proven difficult in the prior art.
One example of how a processing material is used can be found in closed circuit breathing equipment. This equipment, also known as a re-breather apparatus, is frequently used by military and advanced civilian divers, firefighters, and other users who must operate in noxious environments. The advantages of this type of equipment are: (1) superior use time for a given bulk/weight; (2) quiet operation; and (3) bubbles are not released when a user is breathing with the unit in an underwater application.
As the name implies, a user (for example, a diver) breathes in and out on an apparatus in which his/her exhaled gas containing CO2, unused oxygen, and sometimes a diluent gas such as nitrogen, helium, or certain mixtures of inert gases is processed to be available for the next inhalation. The exhaled CO2, which was formed in the diver's body, is retained by a so-called CO2 scrubber, and used oxygen is automatically replaced from a compressed-gas container (or containers) of “make up gas.”
The CO2 is removed by being bound chemically to an absorbent material which can be contained in a scrubber canister. The diver's breathing action moves the exhaled gas through the scrubber and into a rubber or plastic bag. This is often called the re-breathing bag. The absorbent typically comprises a mixture of calcium d-hydroxide and sodium hydroxide fashioned into small pellets, or small gravel-like granules. Once the CO2 has been removed, and make-up oxygen (to replace the oxygen used up in the previous breaths) has been added, the gas in the re-breathing bag is available for the diver's next inhalation. The advantage of this system compared to conventional open-circuit scuba gear is that in the re-breather essentially all the oxygen stored in the compressed gas containers is available for the diver's metabolism while in conventional open-system scuba gear, each expiration, including its content of unused oxygen, is exhaled to the surrounding water.
However, re-breathing gear poses challenges, some of which are: (a) economic and logistic; and (b) tactical and safety related. These challenges are overcome by the presently described technology.
In the prior art, it was not possible to reliably predict how much CO2 absorbing capacity is still available in a scrubber after a dive is completed. This is true regardless of whether the soda lime used is of a color-changing indicator type or non-indicator type. Thus, the user must empty the soda-lime canister and put in a fresh charge of soda-lime before each dive. This is cumbersome and expensive. Note that, after partial use, the indicator soda lime typically returns relatively quickly from its violet or other dark color back to white—termed “blanching.” This is because the CO2 which is bound to the superficial layers of the absorbent granules, causes a change to violet or other dark color before the CO2 binding action of the deeper layers has had time to take place. During non-use periods of the canister, a redistribution of CO2 occurs within the granules which reduces the amount of CO2 bound to the superficial layers. Thus the indicating dye returns to the white color despite the fact that the total absorbing capacity of the granule has been reduced. It is not possible, by visual inspection, before the start of a dive, to determine how much absorbing capacity remains in the absorbent bed.
A user should be able to plan ahead with regard to the potentially available processing material. This is especially true for a diver attempting to plan ahead with regard to the duration of a dive, whether his/her CO2 scrubber canister has just been charged with fresh absorbent or contains absorbent that has been partially used in previous dives. If the CO2 scrubber's unused absorption time is known at any point in time of usage, this information enables the diver to determine whether enough underwater time is available to return to base after a mission. Furthermore, it would allow a diver to plan for a slow enough ascent time to avoid decompression sickness.
Although this problem is described with reference to a re-breather system, the concept of monitoring the processing capacity of a processing material is not limited to this field. There are many other examples where an accurate method of determining processing capacity would be advantageous.